Means for dampening the surface of a rotating cylinder



Oct. 21, 1958 H. A. PRITCHARD 2,856,848

MEANSFOR DAMPENING THE SURFACE OF A ROTATING CYLINDER Filed May 5, 1955[28 HIGH [3 l2 VOLTA 6E SOL/R05 INVEN TOR. HOWd/PO A. W 7' 67% BY I $41MUnited States Patent Ofitice 2,855,848 Patented Oct. 21, 1958 MEANS FORDAMPENING THE SURFACE OF A ROTATING CYLINDER Howard A. Pritchard, Hiram,Ohio, assignor to Harris- Intertype Corporation, Cleveland, Ohio, acorporation of Delaware Application May 5, 1955, Serial No. 506,188

7 Claims. (Cl. 101-147) This invention relates to means for dampeningthe surface of a rotating cylinder, particularly to electrostatic meansfor dampening the lithographic plate cylinder of a printing press, andto means for collecting and reclaiming moisture particlesnot adhering tothe plate.

Most ink repellent solutions used for dampening the plates oflithographic presses are toxic and corrosive. This presents a seriousproblem when the solution is applied to the plate or other rollers ofthe dampening system as a fog, spray or mist. Being of a toxic nature,ink repellent moisture particles suspended in air can be injurious tothe lungs of a press operator, and also can corrode printing press partsto which the moisture particles cling.

One of the objects of this invention therefore is to collect moistureparticles not adhering to the surface of a rotating cylinder to whichmoisture is being applied.

Another object is to provide electrical precipitating means forcollecting excess particles of ink repellent moisture.

Still another object of the invention is to provide an enclosedrecirculating dampening system in which air pressure is utilized tocreate fine moisture particles and assist in directing them into a fieldof force by means of which they are impelled toward and onto a rotatingmember, and in which vacuum is utilized to exhaust those moistureparticles not adhering to the member.

A further object is to provide means for electrostatical- 1yprecipitating moisture along an exhaust line from a dampening area,whereby exhausted moisture particles are prevented from getting into thevacuum pump.

A further object is to reclaim moisture particles which do not adhere tothe lithographic plate of the press.

Another object is to collect stray moisture particles of ink-repellentsolution, which particles have escaped from their normally confined areaby being ejected due to air pressure which is utilized to create themoisture particles.

Still another object is to provide means for returning reclaimedmoisture to its source whereby it may again be used.

According to the invention, an electrical field of force is providedadjacent the surface of a rapidly rotating cylinder. Means including anair pressure line is provided for creating a fine fog of air andmoisture particles and directing it into the field of force. Theelectrical field serves to charge and impel the particles toward andonto the surface of the cylinder. Vacuum exhaust means is provided,eifective in the area of the field of force, to prevent undue buildingup of air pressure in that area and to collect the fog containing thosemoisture particles which do not adhere to the cylinder. Some airpressure is needed to carry the fog to the field of force, but after thefog reaches the field of force the pressure should be dissipated, asotherwise it will carry the fog outward laterally and into theatmosphere surrounding the machine. Both air pressure for creating anddirecting the fog into the field of force and vacuum for exhausting airand fog are preferably provided by the same pump. Means is providedalong the vacuum line for collecting the excess moisture particles,preferably by electrical precipitation, so that they are removed fromthe exhausting air, thus preventing them from contaminating the airaround the press and, where a single pump is used, preventing them fromgetting into the pump. The collecting means may be so arranged that themoisture may be reclaimed.

In the drawing, the figure illustrates a generally schematic elevationaland partially sectional view of a portion of a plate cylinder of alithographic printing press and the preferred means for dampening theplate.

As shown in the figure, a plate cylinder 10 has mounted thereon alithographic plate 11, the ends of which extend into a gap 12. In theembodiment shown, the plate cylinder is electrically grounded as at 13and rotates in a counterclockwise direction. A housing 14 and a pan 15confine a fog created within the housing 14 and containing moistureparticles 16 of ink repellent material. The housing 14 comprises top,rear and end walls. The forward portion of housing 14 comprises asemicylindrical shell 40, the purposes of which will presently appear.

The fog of air and moisture particles 16 is created by a motor-drivenpump 17 which provides air pressure in lines 18 and 19 that extend intothe housing 14. The housing 14 extends the full length of the platecylinder but may be divided into a series of smaller sections ifdesired. In such cases there may be one line 13 and one line 19 providedfor each section. The forward end of line 18 inside the housing 14 is inthe form of a jet or nozzle 9. A tube 20 is connected to line 18 and hasits other end inserted below the level of liquid 21 contained in the pan15, by means of which liquid is drawn into line 18 ahead of the nozzle.Line 19 has an opening 22 directly opposite the jet or nozzle 9 and hasa plug 23 to enclose air within the line 19 except for the opening 22.The fog containing moisture particles 16 is created by the opening 22and nozzle 9 being directed toward each other, line 18 sucking up liquid21 through the tube 20. The blast of air from line 19 and the blast ofair and liquid from line 18 create the fog containing moisture particles16 in the housing 14. Pressure with in the housing 14 causes the fogcontaining moisture particles 16 to flow down and over the liquid in pan15 and to pass through an opening 24 between a forward portion of thehousing 14 and a rebent portion of the pan 15.

Moisture is thus directed into a field of force created by an electrode25 connected by means of wires 26 and 27 to a high voltage source 28grounded at 29. The electrode 25 is shown as being a small diameter wirebut any suitable kind of electrode may be used. The field of forceexists between the electrode 25 and the grounded plate cylinder 10 andserves to electrically charge and impel moisture particles 16 toward andonto the plate 11 of the grounded cylinder 10. It will be noted that thesemicylindrical shell portion 40 of housing 14 is substantiallyconcentric with the electrode 25, and on its forward side constitutes achamber 41 which serves as a charging zone for the moisture particlesand also as a fogconfining area around the electrical field of force.The chamber 41 is provided with end walls, one of which is shown in thedrawing at 42.

Rotary switching means 30 is provided in conductor 26 and is timed withthe rotation of cylinder 10 to turn off voltage to electrode 25 eachtime the gap 12 of cylinder 10 comes opposite the electrode. Thisswitching means may comprise a pair of contact brushes 44 and 45,between which turns a circular wiper 46 with an interrupted segment,that maintains the circuit through conductor 26 during .the major partof each revolution. This serves to minimize the deposition of moistureparticles in the gap where they may accumulate on the mechanism or formdroplets which may be thrown out of the gap by centrifugal force. Theopening and closing of switch means 30 should be so timed that asufiicient amount of dampening solution gets to the edges of the platewhile getting as little as possible into the gap.

A portion 31 of the housing 14 and a portion 32 of the pan 15 lie asclose to the surface of the cylinder as is practical to confine the fogaround the field of force. The housing 1.4 and pan may be of insulatingor conducting material as desired. If made of conducting material, thehousing 14 may be electrically grounded to assist in the collection ofcharged stray moisture particles.

Since there is some space between the portion 31 of housing 14 and thecylinder it), and since cut-off of voltage to the electrode occurs eachtime the gap 12 comes around, and since lines 18 and 19 provide a slightpressure of air within the housing 14, it can be seen that some or" themoisture particles may escape into the atmosphere surrounding the press.By the present invention means is provided 'to collect those moistureparticles. This collection is accomplished by the pump 17 which createsa vacuum through a line 33 communicating with an exhaust chamber 34. Thevacuum through line 33 and the air pressure through lines 18 and 19 arepref erably continuous and as shown are all created by the same pump 17.When the gap 12 is in the position shown in dotted lines, the spacebetween portion 31lof housing 14 and the cylinder iii will be enlargedand will augment the action of the vacuum in relieving air pressure andin drawing away excess fog accumulating around the electrode 25.

To prevent the moisture particles 16 from getting into the pump 17,means is provided along line 33 to electrically collect the moistureparticles. This means is shown on a reduced scale relative to the otherparts of the mechanism. It comprises a second electrode 35 connected towire 27 and a sleeve 36 grounded at 38, the bottom of the sleeve havinga drain tube 3'7 connected thereto and preferably arranged to returnmoisture to pan 15. It can be seen that fog containing moistureparticles evacuated from the chamber will pass through line 33 and thatthe moisture particles will be again electrically charged by theelectrode 35, and be impelled onto the sleeve 36 by a field of forcecreated between the electrode 35 and the grounded sleeve. There theyaccumulate and are conveyed by tube 37 back into the pan 15. As shown,voltage is continually applied to electrode 35 so that themoisture-laden air is cleansed of moisture and may be re irculatedthrough lines 18 and 19.

It should be understood that this invention is equally adaptable toapplying ink repellent moisture particles to a vibrating roller which inturn passes the moisture to a pair of molleton rollers which then passand lay down moisture upon the plate, or to applying moisture to inkingrollers by which the moisture is conveyed to the plate. Also, while theelectrode 25 as shown serves both to charge the particles and to createthe field impelling them toward the plate, the particles may bepreviously charged by separate means and then brought into theelectrical field.

Having thus described my invention, I claim:

1. In a lithographic printing press, an electrically grounded rotatingmember, an electrode parallel to but spaced from said member, a highpotential source of electricity to which said electrode is electricallyconnected, there being an electrical field of force between theelectrode and the grounded member, means for creating a fog containingfinely divided ink repellent moisture particles, said fog being directedinto said field of force and said field of force impelling the particlestoward and onto said grounded member, vacuum creating means, exhaustmeans connected with said vacuum creating means for collecting thosemoisture particles not adhering to the grounded rotating member, andelectrical precipitating means intermediate the point of collection ofmoisture particles and said vacuum creating means for reclaiming themoisture and preventing it from entering said Vacuum creating means.

2. The invention set forth in claim 1 in which the means for creatingthe vacuum also creates air pressure which is utilized in creating thefog.

3. In apparatus for dampening the surface of an electrically groundedrotating cylinder, a wire electrode parallel to but spaced from saidcylinder, at high potential source of electricity, an electricalconnection between said source and said electrode, a shell partiallyenclosing said electrode and open toward said cylinder, means includingan air pump for creating a fog of air and finely divided moistureparticles, means for directing the fog into the field of force betweenthe electrode and the grounded cylinder whereby the moisture particlesin said fog are impelled by said field toward and onto the groundedcylinder, exhaust means for collecting fog including moisture particlesnot adhering to said cylinder, said exhaust means comprising a vacuumline to said air pump, and means for clearing the exhausted fog ofmoisture particles, said last named means comprising electricalprecipitating means.

4. The invention set forth in claim 3 in which the air cleared ofmoisture particles by said electrical precipitating means isrecirculated for creating additional fog.

5. The invention set forth in claim 4 including means for returningmoisture precipitated by said electrical precipitating means to itssource.

6. In a lithographic printing press, an electrically grounded platecylinder having a gap, a lithographic plate mounted on said cylinderwith its ends extending into said gap, an electrode parallel to andadjacent said cylinder, a high potential source of electricity to whichsaid electrode is electrically connected to provide an electrical fieldof force between the electrode and grounded cylinder, means comprising acombination air pressure and vacuum pump for creating a fog of air andfinely divided moisture particles and presenting said fog into saidfield of force whereby said particles are charged and impelled towardand onto said plate, exhaust means connected to the vacuum side of saidpump for collecting fog containing moisture particles not adhering tosaid plate, a second electrode intermediate the point of collection ofsaid fog and said pump for again charging the moisture particles in saidexhausted fog, grounded means on which said recharged particles areprecipitated, and switching means timed with the rotation of saidcylinder to turn ofi electricity to said first electrode each time thegap in said. cylinder comes opposite said field of force between the.

first electrode and the cylinder.

7. In apparatus for dampening the surface of an electrically groundedrotating cylinder, an electrode parallel to but spaced from saidcylinder, a source of high potential electricity, an electricalconnection between said source and said electrode, a shell partiallyenclosing said electrode and open toward said cylinder, means includingan air pump for creating a fog of air and finely divided moistureparticles and for moving said fog under pressure into the shell aroundsaid electrode and into the field of force between the electrode and thegrounded cylinder, whereby the moisture particles in the fog areimpelled by said field toward and onto the grounded cylinder, exhaustmeans efiective in the area of said field of force for lower-' ing theair pressure in said area and for collecting fog including moistureparticles not adhering to said cylinder,

5 and electrical precipitating means for clearing the eX- hausted fog ofmoisture particles, said exhaust means comprising a vacuum line to saidair pump in which said precipitating means is located, whereby the airentering the intake side of said pump is free of moisture.

References Cited in the file of this patent UNITED STATES PATENTS2,551,582 Carlson May 8, 1951 Pethick Apr. 7, 1953 Martin Aug. 30, 1955FOREIGN PATENTS Great Britain Dec. 1, 1954

